26 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



and equidimensional, to long and narrow. It may be located near the 

 center of a shrub, but most often it is located on the outer branches of 

 the host in a fork or near the tip of a leafy branch (figs. 333, 335). 



Several factors seem to influence the shape of the tent. The most 

 important ones may be the life form of the host and, as reported by 

 Wellington (1957, 1960),^ individual differences in the behavior of the 

 larvae making up a colony. His studies on Ai. [californicum] pluviale 

 showed that colonies containing higher percentages of active (Type I) 

 lai'vae tended to build the more elongate tents at or near the tips of 

 branches, and colonies containing fewer active larvae and more sluggish 

 (Type II) larvae constructed more compact and equidimensional tents 

 farther back from the tips of branches or in crotches. He notes that 

 although the opposite t)'pe of tent could have been built in many cases, 

 it was not, and he concludes that the shape of the tent was not limited 

 by the life form of the host. 



In the populations of M. californicum pluviale with wliich Wellington 

 worked there can be little doubt that the types of larvae were the 

 dominant factor influencing the shape of the tent, but it remains to be 

 seen if this holds true for the other species and subspecies. Sullivan and 

 Wellington (1953) found the same different types of larvae for M. 

 americanum and M. disstria as were found for M. californicum pluviale, 

 so there is no reason to believe that these types of laivae would not be 

 found in other species and subspecies. Observations made in the course 

 of this study, however, indicate that the life form of certain hosts 

 also may have a role in determining tent shape and location. 



For example, in the area around San Francisco Bay M. californicum 

 californicum frequently is found on the coast live oak, Quercus agrifolia. 

 This species of oak possesses numerous short, stout twigs near the tips 

 of the branches which, in turn, have m.any stiff leaves projecting in 

 all directions near the ends of the twigs. Tent caterpillars will not eat 

 the old, tough leaves (the preceding year's growth on live oaks), but 

 they make good use of them by frequently constructing their tents 

 over them. This often results in a compact type of tent that is located 

 near the tip of the branch. The new growth is usually only a few inches 

 long, and any of it that is located near the tent may be covered by the 

 tent and/or severely damaged by feeding. There are, of course, some 

 sites that will permit the construction of elongate tents, but these 

 may be in the minority, and thus it is possible that a colony that 

 normally would build an elongate tent may build a more compact 

 one because of the life form of the available site. 



^ Since this was written, Wellington has published additional work on individual 

 differences. See W. G. Wellington, 1967, Can. Ent., 99: 249-263 for references to 

 his papers on this topic. 



